1. Field of the Invention
The present invention relates to systems and methods receiving broadcast signals, and in particular to a system and method for receiving simultaneous terrestrial and satellite broadcasts sharing the same channel using an antenna with posterior sidelobes and anterior nulls.
2. Description of the Related Art
It has been proposed to cooperatively share the current Broadcast Satellite Service (BSS) frequency bands to allow additional programming material to be transmitted to BSS users or subscribers using the same frequency bands as currently used by BSS satellites. This is implemented through the use of terrestrial based transmitters to transmit the additional programming.
One such system is disclosed in U.S. Pat. No. 5,761,605, issued to Tawil et al. on Jun. 2, 1998, which patent is hereby incorporated by reference herein. This patent describes a system in which transmissions from the terrestrial transmitter are received by a second antenna at the user's premises that faces in the opposite azimuthal direction from the BSS satellite receive antenna.
Fundamental to any such system, including the system disclosed in the '605 patent, is that the isolation between the signals from the terrestrial source and the satellite source must be sufficient to prevent interference. While the foregoing system applies to simultaneous channel sharing between satellite and terrestrial transmitters, it requires a BSS satellite ground antenna having highly directional, monocular sensitivity characteristics in order to realize low interference levels. Such antennae can be difficult and expensive to design and produce. Further, it is impractical to replace or modify the several million BSS satellite receive antennae now in use which do not have the desired highly-directional monocular sensitivity. Thus, any simultaneous use of the BSS bandwidth for terrestrial transmissions according to the '605 patent would cause large areas of unacceptably high interference with existing systems.
What is needed is a system and method that provides significantly improved interference isolation to provide simultaneous channel sharing without requiring a satellite ground antenna (e.g. a BSS antenna) with highly directional sensitivity characteristics. Preferably, such a system and method would permit terrestrial re-use of the subject BSS broadcast frequencies, with reduced and more acceptable potential interference levels, particularly when used with standard BSS antennae already in widespread use. The present invention satisfies that need.